Channel selecting circuit



May 9, 1944.

w. H. T. HOLDEN 2,348,626 CHANNEL SELECTING CIRCUIT Fj led Nov.- 14,1942 :5 Shee ts- Sheet 1 FIG.

INVENTOR I4. H. -7.' HOLDEN A T TORNEV y 1944- w. H. T. HOLDEN 2,348,626

I CHANNEL SELECTING CIRCUIT Filed Nov: 14. 1 42 a Sheets-Sheet 2 MARKER cam/m SEA/DER SENDER LINK INVE/V'TOR V W h! 2' HOLDEN ATTORNEY y 9, w. H. T. HOLDEN ,348,626

" CHANNEL SELECTING CIRCUIT Filed Nov. 14, 1942 s Sheets-Sheet s' w -IHI lNl/ENTOI? 8 WH THOLDE/V ATTORNEY Patented May 9, 1944 UNITED STATES PATENT OFFICE CHANNEL SELECTING CIRCUIT Application November 14, 1942, Serial No. 465,573

Claims. (Cl. 179-22) This invention relates to telephone systems and has for its object to facilitate the establishment of connections therein.

In the cross bar system connections are established in two stages, each of which includes the identification of the incoming and outgoing circuits, followed by the identification of three sets of links forming channels over which the incoming and outgoing circuits may be connected, testing these links to select an idle channel and operating the switches to connect the incoming and outgoing circuits by means of the selected idle channel.

The channels of the first stage, located at the originating oilice, connect a district junctor to a trunk and each channel includes a district link, an ofiice junctor and an oflice link, while the channels of the second stage, located at the terminating ofiice, connect the trunk to the called line, each channel including an incoming link, a line junctor and a line link. The operation of each stage is controlled by a marker.

If the channel testing function were removed from the marker, that circuit would be greatly simplified and its holding time would also be decreased.

In accordance with the present invention, means is provided for testing for and selecting an idle channel independent of the marker by the use of gas-filled tubes.

To this end each intermediate link (oifice junctor or line junctor) is provided with a gas-filled tube having a control or starting anode for each incoming link (district link or incoming link) having access to the intermediate link and a control or starting cathode for each outgoing link (oflice link or line link) having access thereto. When testing for an idle channel, the control anodes of idle incoming links serving the calling or incoming circuit are marked and-the control cathodes of idle outgoing links serving the selected trunk or outgoing circuit are marked. A control gap breakdown will occur in the tubes in which both a control anode and a control cathode are marked. In one and only one of the tubes associated with an idle intermediate link a main gap breakdown will occur, in response to which the switches connecting the corresponding links will be operated to complete the desired connection.

- In accordance with one form of the invention the control electrodes are marked by gas-filled tubes individual to the incoming and outgoing links, while in accordance with anotherform of the invention the control electrodes are marked under the control of the hold magnets of the switches having direct access to the incoming and outgoing circuits, for example, the district junctor and the wanted trunk.

The invention will be more clearly understood from a consideration of the following description taken in connection with the drawings in which Figs. 1 and 2 show the form of the invention employing tubes for marking the control electrodes while Fig. 3 shows the form of the invention employing contacts on the hold magnets for the marking.

For an understanding of the operation of the cross bar system as now used, reference may be made to United States Patent 2,235,803, granted to W. W. Carpenter on March 18, 1941.

In the form of the invention shown in Figs. 1 and 2 a schematic set of switches which for convenience may be called district and oifice switches are controlled to connect any one of the incoming circuits It! to I04 to any one of the outgoing circuits I05 to I08. The incoming. circuits NH and I02 appear in horizontal elements 0 and 9 of district primary switch I09 which is in the 0 level of the frame. The vertical elements of switch I69 are connected to the 0 verticals of the secondary switches III, I I2, etc, The horizontals of secondary switch II I in the 0 level connect with the 0 levels of the ofilce primary switches on a plurality of frames, including switch I I3, while the verticals of switch II3, located in the 0 level of the primary ofiice switch frame, connect with the 0 verticals of secondary office switches H5, H6, etc.

This arrangement differs somewhat from that used in practice but does not differ therefrom in theory. It wil1 be apparent that, if in response to a call incoming on circuit IIJI outgoing circuit I is selected, the connection may be completed over a channel including switch I I39, link III, switch III, link H8, switch H3, link H9 and switch I I5; over a channel including switch m9, link I20, switch IIZ, link I2I, switch IIA, link I22 and switch [I5 or over eight other channels, involving other switches, not shown.

In the previous cross bar arrangements, it has been necessary in establishing such a connection to connect each of the links which make up a channel to the marker and then test each link to find an idle channel. This required a large number of relays and complicated the marker circuits.

In the setting up of a connection employing the circuits of Figs. 1 and 2, when a call reaches an incoming circuit IUI, that circuit will be connected over circuits indicated by conductor I23 through the sender link 200 to an idle sender 20L The wanted line designation is set up in the sender which then connects with an idle marker 203 by means of marker connector 202. A part or all of the designation is transmitted to the marker which selects an outgoing circuit, for example, circuit I05, connects with the frame on which that circuit appears and locks out all other markers in a manner similar to that used in the Carpenter patent above mentioned. The marker then prepares the circuit to find an idle channel connecting circuit IilI with circuit I05.

The channel testing arrangement of Fig. 2 employs cold cathode gas-filled tubes as a means of selecting and closing through an idle channel. One tube is provided for each link of each channel.

Since each incoming circuit has access to only ten incoming links, that circuit may control the selection of the ten tubes associated with these incoming links. When the marker is ready for the channel test to take place, it signals the incoming circuit IilI which grounds conductor Hit, leading to the winding of relay 2G5 and battery. Relay 205 identifies the ten links serving incoming circuit IIlI by connecting +100 volt battery to the starting anodes of the tubes belonging thereto. For example, relay 2815 connects battery through resistance 2!]? to the starting anode 206 of tube 208 Which is individual to link I28, and through resistance 209 to the starting anode 2H0 of tube ZII which is individual to link II'I. Hold magnet I3I of the district primary switch I09, when operated, connects ground over conductor I5! in shunt of resistance 239 and hold magnet I32 connects ground to conductor I52 to shunt resistance 20?, so that starting voltage does not reach the starting anodes in the case of busy incoming links.

The starting cathode 2M of tube 283 is connected over conductor I53, back contact of hold magnet I33 of district secondary switch H2, in which link I26 terminates, conductor I54 to ground through resistance 2H3. Starting cathode 2I5 of tube EII is connected over conductor I55, back contact of secondary hold magnet I34 and conductor I55 to ground through resistance ZI'I. Therefore it will be apparent that the starting cathode circuit is open whenever the corresponding link is busy. Furthermore, no current surge can reach the intermediate tubes when busy links are released.

The value of resistances M6, 2H, etc., is such that for idle links a low current, insufiicient to bring about transfer to the main gap, flows through the associated tubes. Tubes 288, 2H, etc., are intentionally so made that transfer does not take place readily, with the purpose of preventing transfer at this time. However, a voltage of approximately +40 volts will exist across resistances 2I-6 and 2H, which voltage is applied to one starting anode in each of the tubes 2I8 and 259 individual to the intermediate links H8 and I2I to which the incoming links H! and 25} have access. Resistance 2H5 associated with incoming link I20 is connected to a starting anode of tube 2I9 individual to intermediate link I2I, while resistance 2H associated with incoming link H1 is connected to a starting anode of tube 2I8 which is individual to intermediate link H3. Resistances H6 and 2H are also connected to starting anodes in tubes not shown which are individual to the intermediate links connecting switches H2 and III to other office frames.

The main anodes of tubes 268 and 2| I are con nected in multiple to alternating current source 230 through common resistance 23I and individual resistances 232, 233, etc. The main cathode 2I3 of tube 208 is connected to the sleeve conductor of link I29 and through the windings of magnets I32 and I33 to central office battery. Similarly the main cathode of tube 2H is connected to the sleeve conductor of link Ill and through the windings of magnets I3I and I34 to battery. With either link busy, ground is connected to the sleeve conductor thereby further preventing transfer by a tube corresponding to a busy link.

When the marker selected the group of outgoing circuits including circuit I05 it operated relay 234 to connect them to the marker for test. Having selected outgoing circuit I 05 and signalled incoming circuit IEII to operate relay 285, the marker closes a circuit from ground over conductor 235, outer left contact of relay 234 to the winding of relay 235 and battery. Relay 236 is individual to the group of trunks I95, I06 and therefore to the group of secondary links I I9, I22, etc., which have access to that group of trunks. Relay 23-5 connects a potential of l00 volts in multiple through individual resistances 231, 238, etc. to the starting cathodes 23:9, 240, etc., of tubes 24!, 242, etc. Tube 245 is individual to link I I 9, having its main cathode 243 connected to the sleeve conductor and through the windings of hold magnets I25 and I26 to battery, while tube 242 is individual to link I22, having its main cathode 244 connected to the sleeve conductor of that link and through the windings of magnets I21 and I28 to battery.

In a manner similar to the arrangement of tubes 2% and 2H, hold magnets I26 and I28 when operated connect ground in shunt of resistances 23! and 238, rendering the starting potential ineffective in the case of busy outgoing links. The main anodes 25.5, 246, etc., of tubes 24], 242, etc., are connected in multiple through resistance 22!) to alternating current source 22I. The starting cathodes 24'! and 249 are connected to ground through resistances 248 and 25!! respectively and these resistances are in turnv connected through high resistances 25l and 252 to the corresponding starting cathodes in tubes 2I8, 2i9, etc., individual to the intermediate links to which the outgoing links have access. Each resistance 248 will be multiplied to ten resistances 2-5I since each outgoing link may be reached over ten intermediate links.

As in the case of tubes 238 and 25 I, tubes MI, 242, etc. andtheir circuits are designed so that a low current flows in the starting gap which is. insufficient to cause the main gap to break down but does cause a potential of 40 volts to appear on the corresponding starting cathodes of tubes 2!.8, 2I9, etc.

Therefore there is a potential of +40 volts on one starting anode in all tubes 2I8, 2I9, etc., individual to intermediate links having access to idle incoming links and a potential of 40 volts on onev starting cathode in all tubes H8, 249, etc., individual tov intermediate links having access toidle outgoing links.

The main anode 253 of tube 2I8 is connected to the winding of relay 2.54 and alternating current source 255 while the main anode 255 of tube 2 I 9V is connected through the winding of relay 251 to source 255. The main cathode 258 of tube 2I8 is connected to battery through the windings of select magnets I62 and I83 which identify the level at which intermediate. link IIfl appears in switches I I I and I I3. Similarly the main cathode 259 of tube 2| 9 is connected to battery through the windings of select magnets I60 and I6I which mark the level of intermediate link I2I in switches H2 and H4.

Each of the tubes 2I8, 2I9, etc., has a pair of grid electrodes. Anode grids 260 and 2BI of tubes 2I8 and 2I9 are connected in multiple through impedance 262 to +100 volt battery. Cathode grid 263 of tube 2I8 is connected through resistance 264 to the sleeve conductor of intermediate link H8 and cathode grid 265 of tube 2I9 is connected through resistance 266 to the sleeve conductor of intermediate link I2I. The ofiice battery having a potential of -50 volts is connected to these sleeve conductors when the links are idle, while ground over the switch contacts marks busy links.

In those tubes 2 I8, 2 I 9, etc., in which a starting anode and a starting cathode are marked by idle incoming and outgoing links, there will be a potential difierence of 80 volts across the start gap and that gap will break down. If the cathode grids 263 and 265 are at 50 volts due to the intermediate links being idle, transfer will take place to these grids, followed by transfer to the gap between the cathodes 258, 259 and the anode grids 260, 26L Since all of the grids 260, 25I, etc., are connected to +100 volts through a common impedance the main gap in one tube will break down and lock out all the remaining tubes.

The breakdown of one main gap, for example in tube 2I8, causes relay 254 and select magnets I62 and I63 to operate. The select magnets prepare the proper levels in the district secondary switch III and office primary switch I I 3. Relay 254 closes a short circuit around resistance 25I and also around the resistances connected to the other starting cathodes of tube 2 I8. This reduction in resistance increases the current flow in the starting gaps of tubes 2H and 2M so that the-main gaps in these tubes will break down.

The breakdown of the main gap of tube 2| I causes the operation of hold magnets I3I and I34. Since the incoming circuit IOI operated the select magnet I30 of the primary switch I09 corresponding to that circuit the incoming circuit I is now connected to intermediate link I I8.

The breakdown of the main gap of tube 24I permits hold magnets I25 and I26 to operate. When the outgoing circuit I was selected by the marker, the select magnet I64 was operated so that the circuit from the incoming circuit to the outgoing circuit I05 is now completed.

The incoming circuit now grounds the sleeve conductor of the operated channel, thereby grounding the cathode 2I2 of tube 2| I. The incoming circuit also releases relay 205 which opens the start gaps of the tubes whose main gaps did not break down. The operation of magnet I3I connects ground to the start anode 2I0 of tube 2 so that, with ground on cathode 2| 2, when alternating source 23I passes through the next half cycle tube 2I I releases.

Similarly, ground on the sleeve of link II9 extends to cathode 243 of tube 24I and magnet I26 connects ground to start cathode 239 resulting in the release of tube 24I on the next half cycle of source 22 I.

The marker receiving an indication that the connection has been completed releases relays 234 and 236 to open the start gaps of the tubes in which the main gaps did not break down. Relay 236 also opens the screen grid circuit of tube 2I8 and this tube also releases, since its main anode supply is alternating current and the control gaps have been deenergized.

It is to be understood that all of the magnets as well as relays 254 and 251 are provided with copper sleeves so that they will function with pulsating current,

This circuit enables the switch frames to find routes from trunk to junctor without extending large numbers of sleeve conductors to the marker and greatly reduces the number of connector relays.

In Fig. 3 is shown an alternative form of the invention.

When a calling subscribers line is extended to an incoming circuit such as circuit 300 and that circuit is connected with a marker, contacts are closed which cause the operation of the select magnet 31' individual to that circuit in the primary incoming switch 3I0. Magnet 30I prepares the cross-points of primary incoming switch 3I0 in which incoming circuit 300 appears and at its right auxiliary contact operates the twenty select magnets 302, 303, etc., which relate to the twenty incoming links 304 and 305 which connect the primary switch 3I0 with the twenty secondary switches 3i I, 3I2, etc. At its left contact magnet 30I connects positive battery to conductor 306. Twenty hold magnets such as magnets 301. and 3I3 are individual to the twenty incoming links 304, 305, etc., extending from primary switch 3I0 to the twenty secondary switches 3II, 3I2, etc. Whenever any one of these links is in use in a connection, the corresponding hold magnet is operated, opening its normal contact. Assuming that both links 304 and 305 are idle, the positive battery connected to conductor 300 is extended over the back contact of the hold magnet 3I3, through resistance M4 to conductor 3I5 and over theback contact of hold magnet 30! through resistance 308 to conductor 309.

At the secondary switch 3 a group of ten incoming links 304, etc., has access to ten intermediate links 320, 32I which appear in the verticals of the switch. The select magnet 302, corresponding to link 304 which extends to the primary switch 3I0 in which the callingv incoming junctor 306 appears, has been operated, as above described. Associated with each intermediate link 320, 32I is a multielement cold cathode tube 322, etc., having separate pairs of starting anodes and starting cathodes, ten such pairs per tube. The starting anodes of these tubes are connected through suitable current limiting resistances to the armatures of the hold magnets corresponding to the incoming links having access to the intermediate link. For example, starting anode 323 of tube 322 is connected over conductor 3I5 through resistance 3M to the armature of hold magnet 3I3 which is individual to incoming link 304. Similarly, starting anode 324 is connected over conductor 325, through resistance 326 to the armature of hold magnet 32! which is individual'to incoming link 32%. Starting anode 345 of tube 343 is connected over conductor 309, and resistance 308 to the armature of hold magnet 301 which is individual to incoming link 305.

The number of the wanted line may be recorded in a sender, the designation transferred to a marker and an idle outgoing circuit selected as described in the Carpenter patent above mentioned. When the idle outgoing circuit has been selected the marker connects ground to the winding of the select magnet individual to the outgoing circuit in the secondary outgoing switch.

Assuming that trunk 329 has been selected, ground will be connected to conductor 330 leading to select magnet 33!, this ground serving to mark the outgoing circuit busy to other markers. Magnet 33l prepares the contacts in the level of secondary outgoing switch 336 in which outgoing circuit 323 appears and also closes at its left contact a circuit for the twenty select magnets 332, 333, etc., one for each of the primary outgoing switches, which are individual to the outgoing links 334, 335, etc. having access to the outgoing circuit selected.

At its right contact magnet 33l connects negative battery to armatures on the hold magnets 33?, 333, etc., of the secondary outgoing switch 336. If outgoing links 334 and 335 are idle, magnets 33'! and 338 will be released and battery will be extended over the back contact of magnet 331, through resistance 339 to starting cathode 349 of tube 322. Similarly, over the back contact of magnet 338, battery is extended through resistance 34| to starting cathode 342 of tube 343 individual to intermediate link 344.

In order that the tubes 322, 343, etc., may be operative the starting electrodes of the tubes must be so arranged that breakdown may be possible from any starting anode to any starting cathode. Any arrangement which would give this result might be used, but according to the preferred arrangement which is suggested by the criss-cross pattern of the drawings, the starting electrodes are made in the form of two groups of ten insulated parallel wires, the wires in one group being at right angles to those in the other, the two groups forming a grid pattern.

As a result of the operations above described, it will be seen that negative battery has been applied to a starting cathode of twenty or less intermediate link tubes 322, 343 and that positive battery has been applied to the starting anode of twenty or less such tubes. If any of the incoming link; or outgoing links are busy, battery will not appear on the starting anodes or cathodes corresponding thereto. In order that one and only one intermediate link tube shall operate, positiv impulses are applied successively to the anode grid leads 343, 341, etc., and negative impulses are applied successively to the cathode grid leads 348, 349, etc., so that the impulse voltages are present at the same time in any one tube, but not simultaneously in more than one tube. The circuit for applying this pulse has not been shown but may be substantially similar to the circuit used in my Patent No. 2,252,766, granted August 19, 1941. Therefore, only one of the tubes 322, 343 will operate, because as soon as one tube operates. the impulse supply to all the grids is shorted out by the grid current flow resulting, If the intermediate link is busy, ground on the cathode of the corresponding tube from the sleeve of the link renders the impulses supplied to that tube ineifec tive. As a result, an idle intermediate link having access to the calling incoming circuit by way of an idle incoming link and also having access to the wanted outgoing circuit, by way of an idle outgoing link is selected by the operation of the tube corresponding thereto. Assuming that tube 322 is operated, intermediate link 320 is selected, this link having access to incoming circuit 399 over incoming link 394 and to outgoing circuit 329 over outgoing link 334.

The main dis harge circuit of tube 322 extends to negative ha y through the of hold magnet 355 of the secondary incoming selector 3| I and through the winding of hold magnet 33! of the primary outgoing selector 352 and these magnets operate. Magnet 350 closes cross-point 353, connecting hold magnet 3I3 of primary incoming selector 3) in parallel with magnet 350. Magnet 313 closes cross-point 354.

Similarly, the operation of magnet 35! closes cross-point 355, connecting hold magnet 33'! of secondary outgoing selector 336 in parallel with magnet 35i, and. magnet 331 operates to close cross-point 353 to complete the connection between incoming circuit 309 and outgoing circuit 329. Hold magnets 313, 350, 35i and 331 are held operated from ground on the sleeve conductor of the incoming circuit 399.

The operation of hold magnets 3l3 and 331 opens the circuits supplying operating voltage to the corresponding starting electrodes, While the incoming circuit responds to the completion of the circuit to outgoing circuit 329 by releasing select magnet 39! and the marker which in turn releases select magnet 33!. Magnets 30! and 33! release the select magnets 302, 333, 332, 333, etc. Tube 322 is also released as the anode circuit .alternating current component now overrides the direct current component.

The diode tube 351 is connected to the sleeve of intermediate link 32!] to prevent reoperation of tube 322 when the circuits release, at which time tube 35'! breaks down and dissipates the energy stored in the hold magnets.

What is claimed is:

1. In a telephone system, incoming circuits, outgoing circuits, a plurality of channels each comprising an incoming link, an outgoing link and an intermediate link for connecting one of said incoming circuits to one of said outgoing circuits, means to identify a particular incoming circuit, means to mark a plurality of idle 11160111.- ing links having access to said identified incoming circuit, means for identifying a wanted outgoing circuit, means for marking a plurality of idle outgoing links having access to said wanted outgoing circuit, a gas-filled tube individual to each intermediate link, a control anode in each tube individual to each incoming link having access to said intermediate link, a control cathode in each tube individual to each outgoing link having access to said intermediate link, a main cathode and a main anode in each tube, means to cause a discharge between a control anode and a control cathode connected to idle incoming and outgoing links having access to the same intermediate link, means to cause adischarge between the main cathode and main anode of one of said tubes in which a control gap discharge occurs and means under the control of said main cathode-anode discharge to establish a circuit between said identified incoming circuit and said wanted outgoing circuit including the intermediate link to which the tube in which said discharge occurs is individual.

2. In a telephone system, incoming circuits, outgoing circuits, a plurality of channels each comprising an incoming link. an outgoing link and an intermediate link for connecting one of said incoming circuits to one of said outgoing circuits, means to identify a particular incoming circuit, m ans to mark a plurality of idle incoming links having access to said identified incomcircuit, means for identifying a wanted outgoing circuit, mcans for marking a plurality of idle outgoing links having access to said wanted outgoing circuit, a gas-filled tube individual to each intermediate link, a control anode in each tube individual to each incoming link having access to said intermediate link, a control cathode in each tube individual to each outgoing link having access to said intermediate link, a main cathode and a main anode in each tube, means to cause a discharge between a control anode and a control cathode connected to idle incoming and outgoing links having access to the same intermediate link, means to cause a discharge between the main cathode and main anode of one of said tubes in which a control gap discharge occurs, means under the control of said main cathodeanode discharge to establish a circuit between said identified incoming circuit and said wanted outgoing circuit including the intermediate link to which the tube in which said discharge occurs is individual and means to prevent a main cathode-anode discharge in tubes individual to busy intermediate links.

3. In a telephone system, incoming circuits, outgoing circuits, a plurality of channels each comprising an incoming link, an outgoing link and an intermediate link for connecting one of said incoming circuits to one of said outgoing circuits, means to identify a particular incoming circuit, first gas-filled tube means to mark a plurality of idle incoming links having access to said identified incoming circuit, means for identifying a wanted outgoing circuit, other gasfilled tube means for marking a plurality of idle outgoing links having access to said wanted outgoing circuit, a multielectrode gas-filled tube individual to each intermediate link, a control anode in each multielectrode tube connected with the first gas-filled tube marking each incoming link having access to said intermediate link, a control cathode in each multielectrode tube connected with the other gas-filled tube marking each outgoing link having access to said intermediate link, a main cathode and a main anode in each multielectrode tube, means controlled by the gas-filled tubes marking idle incoming links and idle outgoing links to cause a discharge between a control anode and a control cathode individual to idle incoming and outgoing links having access to the same intermediate link, means to cause a discharge between the main cathode and main anode of one of said multielectrode tubes in which a control gap discharge occurs, and means under the control of said main cathode-anode discharge to render the first gas-filled tube and the other gas-filled tube connected with the control anode and control cathode of the control gap effective to establish a circuit between said identified incoming circuit and said wanted outgoing circuit including the intermediate link to which the tube in which said main cathode-anode discharge occurs is individual.

4. In a telephone system, incoming circuits, outgoing circuits, a plurality of channels each comprising an incoming link, an outgoing link and an intermediate link for connecting one of said incoming circuits to one of said outgoing circuits, means to identify a particular incoming circuit, first gas-filled tubes individual to the incoming links having access to said identified incoming circuit, each of said first gas-filled tubes having a control gap and a main gap, means responsive to the identification of said incoming circuit to establish a control gap discharge in said first gas-filled tubes individual to idle incoming links, means for identifying a Wanted outgoing circuit, other gas-filled tubes individual to the outgoing links having access to said wanted outgoing circuit, each of said other gas-filled tubes having a control gap and a main gap, means responsive to the identification of said outgoing circuit to establish a control gap discharge in said other gas-filled tubes individual to idle outgoing links, a multielectrode gas-filled tube individual to each intermediate link, a control anode in each multielectrode tube connected with the first gas-filled tube marking each incoming link having access to said intermediate link, a control cathode in each multielectrode tube connected with the other gas-filled tube marking each outgoing link having access to said intermediate link, a main cathode and a main anode in each multielectrode tube, means responsive to the control gap discharge in the gas-filled tubes marking idle incoming links and idle outgoing links to cause a discharge between a control anode and a control cathode individual to idle incoming and outgoing links having access to the same intermediate link, means to cause a discharge between the main cathode and main anode of one of said multielectrode tubes in which a control gap discharge occurs, means responsive to said main cathode-anode discharge to cause a main gap discharge in the first gas-filled tube and the other gas-filled tube connected with the control anode and control cathode of the associated control gap, and means responsive to the main gap discharges in said first gas-filled tube and said other gas-filled tube to establish a circuit between said identified incoming circuit and said wanted outgoing circuit including the intermediate link to which the tube in which said main cathode-anode discharge occurs is individual.

5. In a telephone system, an incoming circuit, outgoing circuits, a plurality of channels each comprising primary and secondary cross bar incoming selectors, primary and secondary cross bar outgoing selectors and an intermediate link for connecting an incoming circuit to one of said outgoing circuits, select magnets and hold magnets for each of said selectors, means under the control of said incoming circuit to operate the select magnets of the primary and secondary incoming selectors having access to said incoming circuit, selection control equipment, means in said selection control equipment to select an idle one of said outgoing circuits and to operate the select magnets of the primary and secondary outgoing selectors having access to said outgoing circuit, a gas-filled tube individual to each intermediate link, a control anode in each tube individual to one hold magnet in each primary incoming selector having access to the corresponding intermediate link, a control cathode in each tube individual to one hold magnet in each secondary outgoing selector having access to the corresponding intermediate link, a main cathode anda main anode in each tube, means controlled by idle ones of said hold magnets to cause a discharge between a control anode and a control cathode, means to cause a discharge between the main anode and main cathode of one of said tubes in which a control gap discharge occurs, and means under the control of said main cathode-anode discharge to operate the hold magnets of the incoming and outgoing selectors of the channel including the corresponding intermediate link to establish a circuit between said incoming circuit and said selected outgoing circuit.

WILLIAM H. T. HOLDEN. 

